Device for optically scanning and measuring an environment

ABSTRACT

A device for optically scanning and measuring an environment, which is designed as a laser scanner, with a light emitter, which emits an emission light beam, with a light receiver which receives a reception light beam which is reflected from an object (O) in the environment of the laser scanner or scattered otherwise, and with a control and evaluation unit which, for a multitude of measuring points (X), determines at least the distance to the object (O), the laser scanner has a swivel-axis module which, as a pre-assembled assembly, on the one hand is provided with a base resting in the stationary reference system of the laser scanner and, on the other hand, with parts which can be fixed to a carrying structure of the measuring head which is rotatable relative to the base.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of German Patent Application No. DE10 2010 032 725.5, entitled “DEVICE FOR OPTICALLY SCANNING AND MEASURINGAN ENVIRONMENT,” filed Jul. 26, 2010, and of U.S. Provisional PatentApplication No. 61/380,416, entitled “DEVICE FOR OPTICALLY SCANNING ANDMEASURING AN ENVIRONMENT,” filed Sep. 7, 2010, both of which areincorporated herein by reference in their entirety.

BACKGROUND

The invention relates to a laser scanner. By means of a device such asis known for example from DE 20 2006 005 643 U1, and which is designedas a laser scanner, the environment of the laser scanner can beoptically scanned and measured.

The invention is based on improving a laser scanner.

SUMMARY OF THE INVENTION

The components of the laser scanner are arranged in two parts of themeasuring head and in a traverse of the carrying structure, whichconnects said parts. In order to reduce weight of the laser scanner, ashell is provided as part of the housing, preferably one shell for eachof the two parts of the measuring head, wherein said shell can be madeof a light material, for example plastic material, and covers thecorresponding components of the laser scanner in order to protect them.To protect the shell in turn, a yoke is provided, preferably one yokefor each of the shells, which partially covers the outside of the shelland which can be made of a light material, for example aluminum, aswell.

The carrying structure, which, for weight purposes, preferably is madeof aluminum as well, preferably has walls, which serve for fixing thecomponents with the optics and the rotating mirror. The walls can alsoclose the semi-open shells. The yoke preferably extends along the outeredges and/or diagonally over the outer surfaces of the shell and isfixed to the carrying structure, preferably at its ends, if and whennecessary also in its center, at one of the two walls. In addition tothe protective function, also further functions can be integrated intothe yoke.

The parameters of the laser scanner, particularly temperature, canchange during operation. Comparative measuring is necessary for acorrection. It is suggested to move the spot of the emission light beamtemporarily along a prism, which has a known geometry and a knowndistance to the center of the laser scanner. The prism additionally hasat least two different brightness levels and/or colors, in order togenerate different signal levels of the reception light beam. Thedifferent brightness levels and/or colors alternate preferably along thedirection of motion of the spot of the emission light beam.

During the rotation of the mirror, the emission light beam is projectedonto the traverse of the carrying structure once during every turn,without the environment below being able to be measured. The prismtherefore is preferably configured at the traverse. A particulargeometrical shape, perpendicular to the direction of motion of the spotof the emission light beam (or in direction of motion), can take accountof the imaging properties of the receiving optics and thus control theresulting signal quality. By means of the different brightness levelsand/or colors and the known distance of the prism, the control andevaluation unit carries out a (correction of the) distance correction.

For assembling the laser scanner the components have mechanical andelectrical interfaces. Particularly between the parts, which arerotatable relative to one another, a high precision is required then.The laser scanner therefore is provided with a swivel-axis module,which, as a pre-assembled assembly, on the one hand is provided with thebase resting in the stationary reference system of the laser scannerand, on the other hand, with parts which can be fixed to the carryingstructure of the measuring head, which is rotatable relative to thebase. The interfaces, which are rotatable relative to one another, arethen displaced into the interior of the interface module. The interfacesbetween the swivel-axis module and the further parts of the measuringhead can be configured (more) simply, so that, when inserting theswivel-axis module, for example into a receiving slot of the carryingstructure, they are closed in the direction of insertion.

In the laser scanner, the motors for rotating the measuring head and themirror, as well as the control and evaluation unit and the furtherelectronic components generate heat, which must be removed. For thispurpose, the laser scanner is provided with an integrated coolingdevice, based on a ventilation. Hereby, the air is led by an air inletinto a space between the carrying structure and the shell, serving as ahousing, from where it gets through a suction duct, which is sealed withrespect to the interior of the carrying structure, into the interior ofthe cooling device. From there, a fan blows the heated-up air through afurther outlet duct, which is sealed with respect to the interior of thecarrying structure, and through an air outlet to the outside. The heatcan thus preferably be removed without impairing the tightness ofcentral components. One filter at air inlet and air outlet each, avoidsintrusion of dust and coarse dust particles into the spaces and ducts ofthe cooling device. The air inlet and the air outlet are orientated, forexample by means of ribs, in that the air streams point away from eachother, i.e. unintersectedly, into directions which are spread apart aspossibly. The suction duct and the outlet duct, having for example arectangular profile, are connected to the housing of the fan in a sealedmanner. Additionally, if required, the ducts can be completely sealed bymeans of suitable plugs. Each of the preferably two shells is semi-openand closed by a wall of the carrying structure, the air inlet and theair outlet meeting preferably exactly one of the two shells, sealed withrespect to one another and with respect to the space. A sealing of theshells, which are arranged outside, against the carrying structure thusguarantees a complete sealing of the laser scanner. In addition to thisventilation, the cooling device preferably is provided with passivecooling elements, for example cooling fins and/or heat pipes, in orderto transfer heat (from sections of the interior of the carryingstructure) to the active cooling elements. This can be the heat from theelectronics or, if the carrying structure is subdivided into two halveswhich are sealed with respect to one another, the heat from the otherhalf (without active cooling elements) of the carrying structure.

DETAILED DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below on the basis of anexemplary embodiment illustrated in the drawing, in which

FIG. 1 shows a perspective illustration of the laser scanner,

FIG. 2 shows a slightly perspective lateral view of the laser scanner,

FIG. 3 shows the bottom view of the laser scanner,

FIG. 4 shows a section of the laser scanner in the zone of theswivel-axis module,

FIG. 5 shows a perspective partial view of the laser scanner withoutshell,

FIG. 6 shows a partial view of the cooling device with the perspectiveof FIG. 5, and

FIG. 7 shows a schematic illustration of the laser scanner duringoperation.

DETAILED DESCRIPTION

A laser scanner 10 is provided as a device for optically scanning andmeasuring the environment of the laser scanner 10. The laser scanner 10has a measuring head 12 and a base 14. The measuring head 12 is mountedon the base 14 as a unit that can be rotated about a vertical axis. Themeasuring head 12 has a rotary mirror 16, which can be rotated about ahorizontal axis. The intersection point of the two rotational axes isdesignated center C₁₀ of the laser scanner 10.

The measuring head 12 is further provided with a light emitter 17 foremitting an emission light beam 18. The emission light beam 18 ispreferably a laser beam in the range of approx. 300 to 1600 nm wavelength, for example 790 nm, 905 nm or less than 400 nm, on principle,also other electro-magnetic waves having, for example, a greater wavelength can be used, however. The emission light beam 18 isamplitude-modulated, for example with a sinusoidal or with arectangular-waveform modulation signal. The emission light beam 18 isemitted by the light emitter 17 onto the rotary mirror 16, where it isdeflected and emitted to the environment. A reception light beam 20which is reflected in the environment by an object O or scatteredotherwise, is captured again by the rotary mirror 16, deflected anddirected onto a light receiver 21. The direction of the emission lightbeam 18 and of the reception light beam 20 results from the angularpositions of the rotary mirror 16 and the measuring head 12, whichdepend on the positions of their corresponding rotary drives which, inturn, are registered by one encoder each.

A control and evaluation unit 22 has a data connection to the lightemitter 17 and to the light receiver 21 in measuring head 12, wherebyparts of it can be arranged also outside the measuring head 12, forexample a computer connected to the base 14. The control and evaluationunit 22 determines, for a multitude of measuring points X, the distanced between the laser scanner 10 and the (illuminated point at) object O,from the propagation time of emission light beam 18 and reception lightbeam 20. For this purpose, the phase shift between the two light beams18 and 20 can, for example, be determined and evaluated.

Scanning takes place along a circle by means of the (quick) rotation ofthe rotary mirror 16. By virtue of the (slow) rotation of the measuringhead 12 relative to the base 14, the whole space is scanned step bystep, by means of the circles. The entity of measuring points X of sucha measurement is designated scan. For such a scan, the center C₁₀ of thelaser scanner 10 defines the origin of the local stationary referencesystem. The base 14 rests in this local stationary reference system.

In addition to the distance d to the center C₁₀ of the laser scanner 10,each measuring point X comprises a brightness information which isdetermined by the control and evaluation unit 22 as well. The brightnessvalue is a gray-tone value, which is determined, for example, byintegration of the bandpass-filtered and amplified signal of the lightreceiver 21 over a measuring period which is attributed to the measuringpoint X. A color camera can optionally generate pictures, by means ofwhich colors (R, G, B) can be assigned to the measuring points asvalues.

A display device 24 is connected to the control and evaluation unit 22.The display device 24 is integrated into the laser scanner 10, in thepresent case into the measuring head 12 The display device 24 shows apreview of the scan.

The laser scanner 10 has a carrying structure 30, which serves as“skeleton” of the measuring head 12 and at which different components ofthe laser scanner 10 are fixed. In the present case, the metal carryingstructure 30 is made of aluminum and in one piece. Above the base 14,the carrying structure 30 has a traverse 30 a which is visible fromoutside and which, at both ends, carries two walls 30 b, which areparallel to one another and project upwards from the traverse 30 a. Twoshells 32 are configured as a housing, which is open to one side,preferably made of plastic. Each of the two shells 32 covers part of thecomponents of the laser scanner 10 which are fixed to the carryingstructure 30 and is assigned to one of the two walls 30 b, to which itis fixed (sealed with a sealing). The walls 30 b and the shells 32 thusserve as housing of the laser scanner 10.

On the outer side of each of the two shells 32 a—preferably metal—yoke34 is arranged, which partially covers and thus protects the assignedshell 32. Each yoke 34 is fixed to the carrying structure 30, and moreprecisely on the bottom of the traverse 30 a. In the present case, eachyoke 34 is made of aluminum and screwed to the traverse 30 a at the sideof the base 14. Each yoke 34 extends from its fixing point at the bottomof the traverse 30 a obliquely to the next outer corner of the assignedshell 32, from where it extends along the outer edge of shell 32 to theouter corner of shell 32 which is above, on the upper side of shell 32obliquely up to the wall 30 b, a short distance along it (may be with anadditional fixing point), and then mirror-symmetrically to the describedcourse on the upper side of shell 32, obliquely to the other outercorner, along the outer edge of shell 32 to the outer corner of shell 32which is below and obliquely to the other fastening point at the bottomside of traverse 30 a.

The two yokes 34 together circumscribe a (convex) space, within whichthe two shells 32 are completely arranged, i.e. the two yokes 34together project over all outer edges and outer surfaces of the shells32. On top and on the bottom the oblique sections of the yokes 34project over the top and/or bottom of the shells 32, on the four othersides, two sections each extending along an outer edge of the shells 32.The shells 32 are thus protected extensively. Although each of the yokes34 primarily has a protective function, particularly with respect toimpacts which might damage the shells 32 and the components of the laserscanner 10 which are arranged below, further functions can be integratedin one or both of the yokes 34, for example a gripping possibility forcarrying the laser scanner 10 and/or an illumination.

On top of the traverse 30 a a prism 36 is provided, which extendsparallel to the walls 30 b. In the present case, the prism 36 is anintegrally formed (i.e. designed in one piece) component of the carryingstructure 30, but a separate formation and fastening to the traverse 30a is conceivable as well. When the mirror 16 rotates, it directs theemission light beam 18 onto the traverse, and more precisely onto theprism 36, once during each rotation, and moves the spot, which isgenerated by the emission light beam 18, along the prism 36.Perpendicularly to the sense of movement of the spot of emission lightbeam 18, the profile of the prism 36 is designed in such a way that,from the top of the traverse 30 a, two trapezoids pointing downwards aredesigned, from which an isosceles triangle pointing upwards projects.Usually, the spot of the emission light beam 18 is so small that is hitsthe top of the triangle, but illuminates the sides only partially. Thesurface of the prism 36 is designed in such a way that at least twodifferent brightness levels and/or colors are provided along thedirection of motion of the spot of emission light beam 18. For example,the half that is illuminated first can have a high brightness level(“light grey,” “white”), and the half that is illuminated next a lowbrightness level (“dark grey,” “black”). A reverse order or a stripedpattern with several changes of the brightness level is possible aswell.

Due to non-linearities in the electronic components, for example in thelight receiver 21, the measured distances d depend on signal intensity,i.e. brightness, temperature and further parameters. A distancecorrection, which is stored as a function of brightness and is nonlinear, is therefore necessary. Since the prism 36 has a known distanced and known brightness levels, a correction of the distance correctioncan be performed by means of the prism 36, namely online, i.e. duringoperation the influence of temperature and other parameters can becompensated. At the points corresponding to the brightness levels of theprism 36, the difference between the known distance and measureddistance is determined. The correction of the distance correction isperformed by adapting the curve of distance correction to the determineddifference. This correction of distance correction preferably takesplace in the control and evaluation unit 22.

The traverse 30 a has a receiving slot which is open at the bottom, andinto which a swivel-axis module 40 is introduced. The swivel-axis module40 is a pre-assembled assembly, which comprises, on the one hand, partswhich are to be fixed at the carrying structure 30 and, on the otherhand, the base 14—which is rotatable in relation to said parts—and partswhich are fixed to it. The base 14 is provided with a dome 14 a, whichprotrudes upward. A sealing 41 is interposed between the dome 14 a andthe carrying structure 30. A swivel axis 42, which protrudes verticallyupward, is fixed to the dome 14 a, in the present case screwed. Ahorizontally arranged worm gearing 44 is fixed to the swivel axis 42.The swivel axis 42 has an inner head 46, which, by means of a crossedroller bearing 47, bears an outer head 48. A horizontally arrangedencoder disk 50 is fixed to the upper end of the inner head 46, abovewhich the outer head 48 has encoder read heads 52. Besides, slip rings54 for the internal (i.e. which takes place within the swivel-axismodule 40) transmission of data and energy of power supply are providedbetween the inner head 46 and the outer head 48. At the upper end of theouter head 48 and at the lower end of the base 14, electric plugconnectors 55 for the transmission of data and energy from and to themeasuring head 12 are provided.

For interaction with the worm gearing 44 a motor 56 with a planetarygear 57 is provided, which is borne in the carrying structure 30 andwhich drives a worm 58, which meshes with the worm gearing 44. Thedescribed swivel-axis module 40 is introduced into the traverse 30 a, sothat the plug connectors 55 at the outer head 48 are plugged togetherwith suitable counter-contacts, the worm 58 meshes with the worm gearing44, the outer head 48 can be fixed to the carrying structure 30 and asealing 59 comes to lie between the base 14 and the carrying structure30. In the swivel-axis module 40, the swivel axis 42, the worm gearing44, the inner head 46 and the encoder disk 50 are fixed to the base 14,while, rotatably relative to this, the outer head 48 and the encoderread heads 52 are fixed to the carrying structure 30, and the motor 56with the planetary gear 57 and the worm 58 are borne. The measuring head12 is thus rotatable about a vertical axis, relative to the base 14.

The laser scanner 10 has an integrated cooling device 70 which cools bymeans of air flowing through sealed ducts. The cooling device 70comprises a suction duct 72, which preferably is designed with arectangular profile, a fan 74 and an outlet duct 76, which preferably isdesigned with a rectangular profile as well. The fan 74 with its housingis connected to the suction duct 72 and to the outlet duct 76 in asealed manner. The suction duct 72 is arranged between the motor 56 forthe swiveling movement of the measuring head 12 and a motor for therotation of the mirror 16 which is arranged above. The outlet duct 76 isarranged between the motor 56 and the electronics.

The suction duct 72 opens to a (largely) sealed space Z between thecarrying structure 30 and the shell 32. The sealing of the space Z (withrespect to the interior of the carrying structure 30) prevents intrusionof dirt and dust into the interior of the carrying structure. Thecarrying structure 30 has cooling fins 78 next to the motor 56, whichtransfer the heat from the interior of the carrying structure 30 intothe space Z. From outside, the air gets over an air inlet 80, preferablya ventilation grille with ribs, into the space Z. A filter (for examplea filter mat) at the air inlet 80 prevents intrusion of coarse dustparticles and dust into the space Z.

The outlet duct 76 terminates—sealed with respect to the space Z—at anair outlet 82, preferably a ventilation grille with ribs. The air inlet80 and the air outlet 82 are spaced apart from each other and, in thepresent case, are separated by the yoke 34 and configured on the bottomof the shell 32. The ribs of the ventilation grilles are preferablyaligned in such a way that the air flow to the air inlet 80 and from theair outlet 82 point away from one another, i.e. no heated-up air issucked in. Additionally, a heat pipe extends between the area of themeasuring head 12 with the control and evaluation unit 22 and thesuction duct 72, said heat pipe transferring heat to the cooling device70 as well. The fan 74 sucks in air via the air inlet 80, the space Zand the suction duct 72 and blows the air again out of the laser scanner10, via the outlet duct 76 and the air outlet 82. Cooling thus takesplace.

The laser scanner 10 preferably has different sensors, for examplethermometer, inclinometer, altimeter, compass, gyroscopic compass, GPS,etc. which are preferably connected to the control and evaluation unit22. By means of said sensors the operating conditions of the laserscanner 10 are monitored, which are defined by certain parameters, forexample geometric orientation or temperature. If one or severalparameters have a drift, this is recognized by the corresponding sensorsand can be compensated by the control and evaluation unit 22. By meansof said sensors, also a sudden change of operating conditions can berecognized, for example an impact on the laser scanner 10 which changesits orientation, or a displacement of the laser scanner 10. If theextent of said changes cannot be registered with sufficient precision,the scanning process must be interrupted or aborted. If the extent ofsaid changes of operating conditions can be roughly estimated, themeasuring head 12 can be turned back by some angular degrees (untilthere is an overlapping with the area which has been scanned before thesudden change), and the scanning process continues. The two differentparts of the scan can be assembled by an evaluation of the overlappingarea.

1. A device for optically scanning and measuring an environment, thedevice being designed as a laser scanner with a light emitter whichemits an emission light beam, with a light receiver which receives areception light beam which is reflected from an object (O) in theenvironment of the laser scanner or scattered otherwise, and with acontrol and evaluation unit which, for a multitude of measuring points(X), determines the distance to the object (O), characterized in thatthe laser scanner has a swivel-axis module which, as a pre-assembledassembly, on the one hand is provided with a base resting in thestationary reference system of the laser scanner and, on the other hand,with parts that can be fixed to a carrying structure of the measuringhead which is rotatable relative to the base.
 2. The device according toclaim 1, characterized in that the swivel-axis module has a swivel axiswhich is fixed to the base.
 3. The device according to claim 2,characterized in that the swivel-axis module has a worm gear which isparticularly fixed to the swivel axis and which meshes with a worm,which is driven by a motor which is particularly borne in the measuringhead.
 4. The device according to claim 1, characterized in that theswivel-axis module is provided with an inner head, which particularly isfixed to the base, and with an outer head, which is rotatably mountedrelative to the inner head, particularly by means of a crossed rollerbearing.
 5. The device according to claim 4, characterized in that theswivel-axis module is provided with an encoder disk which particularlyis fixed to the inner head, and with at least one encoder read headwhich is rotatable relative to the encoder disk and which isparticularly fixed to the outer head and/or that the swivel-axis modulehas slip rings between the parts which are rotatable with respect to oneanother, for the internal transmission of data and energy and/or plugconnectors for the transmission of data and energy from and to themeasuring head.
 6. The device according to claim 1, characterized inthat the swivel-axis module is introduced into a receiving slot of acarrying structure, particularly of a traverse of the carryingstructure.
 7. The device according to claim 6, characterized in that themechanical and electrical interfaces between the swivel-axis module andthe parts of the laser scanner which are fixed to the carrying structureare closed by the introduction of the swivel-axis module into thereceiving slot.